“…Moreover, a growing body of literature on the relationship between academic achievement and the concentration of poverty within a school has demonstrated that the effects of high concentrations of poverty often extend beyond the effects of an individual's poverty (Banks, 2001;Orfield & Lee, 2005;Vanderhaar, Muñoz, & Rodosky, 2006). Many studies operationalize collective SES using single variables, such as residing in social housing (Martens et al, 2014) or by simply asking principals what percentage of their students were of low SES, average SES, or high SES and then calculating a heterogeneity index similar to the Blau index of racial diversity or Simpson's index (1949) in ecological studies (Menzer & Torney-Purta, 2012) while others use a combination of multiple and varied factors.…”